Physics Tip Sheet #14 - May 22, 2002

To investigate the process of mechanical wear, which affects both diesel engines and nanomachines, physicists carved a microscopic trench and found that the accumulated atomic debris had surprising order. The researchers also measured the energy that went into vibrating the crystal surface and into ripping out atoms. Experts say the work shows new details of the wear process and demonstrates a level of control that might be used for micromachining.

Researchers have experimentally shown that information can be written in three-dimensional crystals at densities of greater than 100 terabits/cm^3 (1 Terabit = 10^12 bits). The microfabrication works on a scale of 0.2 micrometers. The recording uses a combination of direct laser writing and a holographic technique that turns converts one ultrashort-pulsed laser beam into four beams, which interfere to create the desired pattern.

Recent reports of slowing and stopping light have opened possibilities of enhanced communication and information processing schemes. A proposed new technique allows similar possibilities but is operable at room temperatures rather than the required 5 kelvin temperatures of the original scheme. The new scheme also works with lower laser powers and is tunable in frequency thereby improving the chances of implementation in commercial communications technology.

Recent experimental studies suggest that there is evidence for synchronization between human heartbeats and respiration. The authors develop a physiologically plausible model for this cardiorespiratory synchronization. In their model, in addition to the well-known influence of respiration on heartbeat, the influence of heartbeat (and hence blood pressure) on respiration is also important for cardiorespiratory synchronization.

Artificial neural networks that are trained on a time series are supposed to achieve two abilities: first, to predict the series many time steps ahead and, second, to learn the rule that has produced the series. The authors show that prediction and learning are not necessarily related to each other. Chaotic sequences can be learned but not predicted while quasiperiodic sequences can be well predicted but not learned.

Experiments are being constructed to "listen" to the universe through gravity waves. However, understanding what is heard depends on models of how various astronomical objects resonate. This paper investigates black hole collapse and collision and finds that after an initial loud gravity wave, there may be persistent loud ringing that can be detected.

The possibility that spacetime is extended beyond the familiar four dimensions has intrigued physicists for a century. Indeed, the consequences of a dimensionally richer spacetime would be profound. Recently, new theories with higher dimensional spacetimes have been developed to resolve the hierarchy problem in particle physics. These scenarios make distinct predictions that allow for experiment to probe the existence of extra dimensions in new ways. The authors review the conceptual framework of these scenarios, their implications in collider and short-range gravity experiments, their astrophysical and cosmological effects, as well as the constraints placed on these models from present data.